Amendment I
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.

"Free Exercise Clause refers to the section of the First Amendment italicized here:

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof...

The Free Exercise Clause reserves the right of American citizens to accept any religious belief and engage in religious rituals. The wording in the free-exercise clauses of state constitutions that religious '[o]pinion, expression of opinion, and practise were all expressly protected' by the Free Exercise Clause.The clause protects not just religious beliefs but actions made on behalf of those beliefs. More importantly, the wording of state constitutions suggest that 'free exercise envisions religiously compelled exemptions from at least some generally applicable laws.' The Free Exercise Clause not only protects religious belief and expression; it also seems to allow for violation of laws, as long as that violation is made for religious reasons. In the terms of economic theory, the Free Exercise Clause promotes a free religious market by precluding taxation of religious activities by minority sects".

Shall I put this in simple English for Trump supporters?

You cannot ban any religion in the United States of America!

Look, I am not a supporter of Islam. I believe Muslims will spend Eternity in Hell. For that matter, I believe most Baptists, Methodists and other Protestants will do likewise, but I wouldn't consider a ban on those heresies either. There's only one way to salvation and that's through Jesus Christ via His one and only Church - The Catholic Church. If that hurts your feelings, I'm sure you'll want to ban my Right to Free Speech as well.